When testing hybrid vehicle or even completely electrically driven vehicles, testing the traction battery is of particular importance. In the process of this, the test current should follow predetermined test cycles with highly-dynamic transients as exact as possible and without delay. This can be achieved via an adequate control loop which is created by means of a model-based controller design method.
The current control is not to be influenced by the unit under test, if possible. However, since the counter-voltage of the device under test depends substantially on the impressed current, i.e., the controlled variable, the latter has a significant influence on the dynamic properties of the control loop. In order to reduce this influence, there is a plurality of possibilities. On the one hand, the power electronics can be designed to have an output impedance as high as possible. However, this results in a reduction of the achievable control bandwidth and involves increased material costs and increased space requirement because this requires larger inductors. In the method of feedforward disturbance control, the measured counter voltage of the unit under test is regarded as a disturbance variable and is used for compensating the disturbance. In this case, however, it is assumed that the disturbance variable is independent of the controlled variable. However, due to the finite battery impedance, the terminal voltage of a battery depends in fact on the impressed current. The behavior of the disturbance variable in response to changes in the impressed current thus cannot be predictively compensated.